> From: Piotr Galka > Sent: Friday, April 27, 2007 5:11 AM > > Hi Peter, > > Having no experience I have one way of understanding the > standards - take the text literally. I also expect that if > any problems arise the text will be taken literally. I know, > that even I ask any experienced agency the whole > responsibility for the product is only mine. So when they > tell me the intention was other should I follow it ? The > intention isn't written in standard.
Hi, Piotr. Your approach is a good one. The problem is with the standard. Even before IEC60950-1:2005 was published, there were proposed corrections to the Creepage Distance tables we discussed a few months ago. I suspect it was intended that §1.5.9.2 was to apply only to those circuits where transients are known safety concerns: ac mains and exposed tnv. I have no hard evidence for this assertion, but it's what makes the most sense to me. > I have asked about PTC, because I prefer them over fuses but > recently I was told, that PTC can't be understand as > interrupting device, as it makes no permanent interruption. Whether or not a PTC is suitable depends entirely on its application (see §2.5, ¶ b. The response you received may have been based on how you asked teh question and the assumptions made by the responder. If you asked about using a PTC to comply with §1.5.9.2, the responder may have assumed you intended teh VDR to be in a primary circuit, in which case, a PTC might not be suitable. PTCs are often used in conjunction with VDRs to meet CSA an UL power cross requirements for on TNV-1 and TNV-3 circuits. > >> If not the fuse with what approval should I look for ? > > > > I don't understand this question. Can you be more specific? > > Asking that I had in mind: > If EN 60950-1 needs me to use here (or anywhere else) an > adequate interrupting device, and I decide to use fuse, can > it be any fuse which in my opinion is good, or I have to > check the fuse manufacturer for some agency reports that the > fuse comply with any particular component standard, and what > standard ? As the standard is written, it's left open. You only need to chose a device that provides 'adequate' protection. Considering your application is in a secondary circuit and if you can demonstrate what levels of current are involved during the transient events your protecting your equipment from, it may be that a PTC is 'adequate.' Another approach you might think about relates to §1.5.9.2, Note 2. This explanatory note relates to increases in leakage current over time. Contrary to my earlier reading, I'm now leaning towards this note referring to leakage current through the device, rather than protective earth currents (it would be most useful, if someone who sat in on this decision can post a response). Consider demonstrating (by test) that the board you mount the device on can withstand currents up to LPS limits with the VDR shunted. Regards, Peter L. Tarver, PE [email protected] CONFIDENTIALITY This e-mail message and any attachments thereto, is intended only for use by the addressee(s) named herein and may contain legally privileged and/or confidential information. If you are not the intended recipient of this e-mail message, you are hereby notified that any dissemination, distribution or copying of this e-mail message, and any attachments thereto, is strictly prohibited. If you have received this e-mail message in error, please immediately notify the sender and permanently delete the original and any copies of this email and any prints thereof. ABSENT AN EXPRESS STATEMENT TO THE CONTRARY HEREINABOVE, THIS E-MAIL IS NOT INTENDED AS A SUBSTITUTE FOR A WRITING. Notwithstanding the Uniform Electronic Transactions Act or the applicability of any other law of similar substance and effect, absent an express statement to the contrary hereinabove, this e-mail message its contents, and any attachments hereto are not intended to represent an offer or acceptance to enter into a contract and are not otherwise intended to bind the sender, Sanmina-SCI Corporation (or any of its subsidiaries), or any other person or entity. _____________________________________________________________________________ Scanned by Sanmina-SCI eShield _______ _____________________________________________________________________ - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________
